Australian John van Wisse has encountered an unexpected obstacle in his ambitious ultra-triathlon bid from London to Paris: the UK border patrol.

Van Wisse, who is on track to break the record for one of the world’s toughest sporting challenges, was briefly mistaken for an illegal immigrant as he prepared to begin the swim leg across the English Channel on Wednesday.

Police and coastguards were called to Dover’s Shakespeare Beach by concerned locals around 8.30am but quickly saw the funny side when they realised what they were dealing with.

A Kent police spokeswoman told the Dover Express: “It looks like a couple of people called thinking it was illegal immigrants coming ashore because some people were seen jumping off a boat.

“The Border Force were down there and the coastguard.

“But it was a Channel swimmer.”

Van Wisse, 41, on Tuesday set off on the “Arch to Arc” challenge, from London’s Marble Arch to the Arc de Triomphe in Paris.

The Victorian had already run 140km from London to Dover before embarking on a 34km swim across the Channel after a break of around seven hours.

He must then cycle 290km to Paris and is currently on track to better the record of 73 hours and 39 minutes, set by Englishman Mark Bayliss in 2012.